The open end of canbodies is commonly reduced in diameter and flanged. The flange facilitates attaching a closure to the end and the reduction in diameter allows using a smaller closure thereby saving material. Furthermore, reducing the diameter does not substantially decrease the volume of the can.
In a production line situation, cans are commonly reduced in diameter by being forced into a tapered necking die. The end of the can is then flanged outward by a plurality of flanging rollers mounted on a flanging head.
A major source of defective cans, the split flange, results from this necking and flanging operation. During the formation of the can, substantial strain hardening takes place. A further reduction in ductility results from the necking operation. When radial forces are then applied to the neck in the flanging operation, cracking and wrinkling may occur.
As noted above, conventional flanging heads carry a plurality of rollers. These rollers are mounted with the axis of rotation parallel to the canbody's longitudinal axis and the head is likewise rotatably mounted. The rollers are uniform in design and have a small diameter at the end which first enters the canbody and a gradually increasing diameter which forms the flange. An example of conventional rollers may be found in FIGS. 2 and 4 of U.S. Pat. No. Re. 30,144 Gnyp, et al.
These conventional rollers have a number of problems. In operation their tapered shape wipes or wedges the canbody outward by longitudinal and rotational motion relative to the canbody. The high forces required for this operation result in frequent maintenance of the rollers. As the rollers must sustain axial loading, the design is somewhat complex and difficult to dismantle and repair. The high forces placed on the canbody may cause defects in other portions of the canbody than the flange, such as scratching of coating off the bottom where the canbody is supported.
Further, as should be apparent to one skilled in the art, the conventional roller configuration shown in Gnyp, et al. results in some relative motion between the rollers and the canbody over a major portion of the contact areas. It is thought that the portion of the roller supporting and contacting the neck rolls without slippage around the neck of the canbody. The outer portion of the roller must then travel at a considerably greater speed resulting in slippage and the generation of frictional forces in the circumferential direction over the area being flanged. These frictional shear forces are thought to weaken the metal and significantly contribute to the problem of defective cans.
The present invention relates to a new and simpler design of head and roller configuration which minimizes shear forces by reducing circumferential slippage between the roller and the canbody over the total contact area and substantially reduces the forces which the canbody is subjected to thereby reducing maintenance and other defects in the canbody.